1. Field of the Invention.
The present invention relates to the field of holography, and more particularly to methods and apparatus for creating two-dimensional holographic patterns.
2. Prior Art
Holographic images have been a source of wonder and amusement for a number of years. Holographic images create the impression of a three-dimensional object from the illumination of a two-dimensional hologram. Holographic images have also been used for various practical applications wherein their unique characteristics readily distinguish the same from conventional images. In that regard, probably the best known example at the present time is the holographic image of a dove used on credit cards for authentication purposes. In particular, the advantage of using a hologram to provide a readily recognizable holographic image is that the same is not reproducible by ordinary printing or photographic processes. The difficulty with such holograms, however, is that they are relatively expensive to first produce, and not particularly inexpensive to reproduce in quantity, thereby tending to limit their application for authenticating items to those things of sufficient value to justify the costs involved. In comparison, there are a large number of items of lesser value which, without some similar authenticating marking, are frequently counterfeited and used, to the very substantial loss of the issuer. Such things include tickets and passes of all kinds, including tickets for sporting events, passes for public transportation, etc. In the cases of these examples, the counterfeit copies are offered to a relatively unsophisticated ticket taker or bus driver under circumstances not allowing significant time and attention to evaluate the same, so that the quality of the counterfeit copy need not be that good to have a high likelihood of being accepted. While the addition of color to tickets in past years has helped, the increased popularity of color copiers has more recently offset that gain. If, on the other hand, like the credit card, such items could be authenticated by an appropriate hologram at a reasonable cost, the genuine item would be quickly recognizable by the casual observer, and would be too costly and difficult to reproduce in small quantity for counterfeiting purposes. Further, if the hologram could be changed frequently, such as by way of example changed for each sporting event, or changed monthly for a one month transportation pass, authentication becomes even easier at the time of use of the ticket, pass, etc., and more difficult for the would-be counterfeiter to reproduce.